He was the son of an ex-officer in the army who belonged to the petite noblesse and adopted the principles of the Revolution. His love of soldiering soon showing Itself, his father took him to Dijon to learn mathematics prior to entering the artillery, and there he made the acquaintance of Bonaparte, which he renewed after obtaining his commission when he served in Toulon.
The acquaintance ripened into intimacy; Marmont became General Bonaparte's aide-de-camp, remained with him during his disgrace and accompanied him to Italy and Egypt, winning distinction and promotion to general of brigade. In 1799 he returned to Europe with his chief; he was present at the coup d'état of the 18th Brumaire, and organized the artillery for the expedition to Italy, which he commanded with great effect at Marengo. For this he was at once made general of division. In 1801 he became inspector-general of artillery, and in 1804 grand officer of the Legion of Honour, but was greatly disappointed at being omitted from the list of officers who were made marshals.
In 1805 he received the command of a corps, with which he did good service at Ulm. He was then directed to take possession of Dalmatia with his army, and occupied Ragusa. For the next five years he was military and civil governor of Dalmatia, and traces of his beneficent régime still survive both in great public works and in the memories of the people. In 1808 he was made duke of Ragusa, and in 1809, being summoned by Napoleon to take part in the Austrian War, he marched to Vienna and bore a share in the closing operations of the campaign. Napoleon now made him a marshal and governor-general of all the Illyrian provinces of the empire.
In July 1810 Marmont was hastily summoned to succeed Masséna in the command of the French army in the north of Spain. The skill with which he maneouvred his army during the year he commanded it has been always acknowledged. His relief of Ciudad Rodrigo in the autumn of 1811 in spite of the presence of the English army was a great feat, and in the mannuvring which preceded the battle of Salamanca he had the best of it. But Wellington more than retrieved his position in the battle, and inflicted a severe defeat on the French, Marmont himself being gravely wounded in the right arm and side.
He retired to France to recover, and was still hardly cured when in April 1813 Napoleon, who soon forgot his fleeting resentment for the defeat, gave him the command of a corps. With it he served at the battles of Lützen, Bautzen and Dresden, and throughout the great defensive campaign of 1814 until the last battle before Paris, from which he drew back his forces to the commanding position of Essonne. Here he had 20,000 men in hand, and was the pivot of all thoughts. Napoleon said of this camp of Essonne, "C'est la que viendront s'addresser toutes les intrigues, toutes les trahisons; aussi y ai-je placé Marmont, mon enfant elevé sous ma tente." Marmont then took upon himself a political role which has, no doubt justly, been stigmatized as ungrateful and treasonable. A secret convention was concluded, and Marmont's corps was surrounded by the enemy. Napoleon, who still hoped to retain the crown for his infant son, was prostrated, and said with a sadness deeper than violent words, "Marmont me porte le dernier coup."
This act was never forgiven by Marmont's countrymen. On the restoration of the Bourbonss he was indeed made a peer of France and a major-general of the royal guard, and in 1820 a knight of the Saint Esprit and a grand officer of the order of St Louis; but he was never trusted. He was the major-general of the guard on duty in July 1830, and was ordered to put down with a strong hand any opposition to the ordinances. Himself opposed to the court policy, he yet tried to do his duty, and only gave up the attempt to suppress the revolution when it became clear that his troops were outmatched. This brought more obloquy upon him, and the due d'Angouleme even ordered him under arrest, saying, "Will you betray us, as you betrayed him?" Marmont did not betray them; he accompanied the king into exile and forfeited his marshalate thereby. His desire to return to France was never gratified and he wandered in central and eastern Europe, settling finally in Vienna, where he was well received by the Austrian government, and strange to say made tutor to the duke of Reichstadt, the young man who had once for a few weeks been styled Napoleon II. He died at Venice on the 22nd of March 1852.
Much of his time in his last years was spent upon his Mémoires, which are of great value for the military history of his time, though they must be read as a personal defence of himself in various junctures rather than as an unbiased account of his times. They show Marmont, as he really was, an embittered man, who never thought his services sufficiently requited, and above all, a man too much in love with himself and his own glory to be a true friend or a faithful servant. His strategy indeed tended to become pure virtuosity, and his tactics, though neat, appear frigid and antiquated when contrasted with those of the instinctive leaders, the fighting generals whom the theorists affect to despise. But his military genius is undeniable, and he was as far superior to the mere theorist as Lannes and Davout were to the pure dimsionnaire or "fighting" general.
His works are Voyage en Hongrie, etc. (4 vols., 1837); Voyage en Sidle (1838); Esprit des institutions militaires (1845); Cesar; Xenophon; and Mémoires (8 vols., published after his death in 1856). See the long and careful notice by Sainte-Beuve, Causeries du Lundi, vol. vi.